(1) Field of the Invention
The present invention relates to test apparatus and, more particularly, to an apparatus employing a microprocessor for adjusting and testing the operating point for proper operation of a current sensor employing a Hall Effect switch.
(2) Background Art
Current sensing devices employing an electromagnetic coil and a Hall Effect switch have been previously disclosed under U.S. Pat. Nos. 4,166,928 ('928) and 4,191,859 ('859) issued Sept. 4, 1979 and Mar. 4, 1980, respectively, both to Sabon. Such devices are useful in detecting the presence or the absence of a telephone subscriber loop before and after ringing current is applied to the loop. Also known in the art are test circuits which detect failures of Hall Effect device operate and release points. Such test circuits are described under U.S. Pat. No. 4,488,112 ('112) issued Dec. 11, 1984 to Thompson et al. and U.S. Pat. No. 4,491,794 ('794) issued Jan. 1, 1985 to Daley et al. Such test circuits apply an electromagnetically generated varying field to the Hall Effect switch and verify either in an analog manner as in patent '112 or in a digital manner as in patent '794 that the Hall Effect switch switches only above a certain magnetic field intensity and below a second greater magnetic field intensity.
Also known is a method and apparatus for adjusting magnetic coupling between a Hall Effect switch and a permanent magnet which is described under U.S. Pat. No. 4,156,191 issued May 22, 1979 to Knight et al. This patent teaches a method and apparatus for setting the relationship between the magnetic flux of a permanent magnet and a Hall Effect switch by demagnetizing the magnet.
The above devices, while related to the present invention do not address the problem of adjusting and testing for proper operation, a current sensing device employing a Hall Effect switch operated by a magnetic field generated by a magnetic circuit employing an electromagnetic coil driven by the sensed current.
Accordingly, it is object of the present invention to provide an adjustment and test apparatus which provides a new and useful method of adjusting and testing for proper operation, electromagnetic current sensors of the type described in the '928 and '859 patents.